Here is a field of triticale with a pathogen I have not seen before. I noticed these diamond-shaped lesions with a yellow border and dark brown spot in the center of lower leaves. It is called Tan Spot (Yellow leaf spot or Blotch) and is caused by Pyrenophora (Syn. Drechslera) spp. Disease development is favored by frequent rains and cool, cloudy, humid weather. I also noticed some of the leaf tips dying – this is also a symptom.
UGA Extension Pathologist Dr. Alfredo Martinez has this information:
The disease is more problematic susceptible varieties, poor fertility and in fields with wheat residue left on soil surface. Initial infections come from diseased crop debris in the soil, or from diseased grass hosts. Usually the lower leaves are infected first, and the disease progresses to the upper leaves and leaf sheaths if conditions are favorable. This disease develops over a wide range of temperatures and is favored by long periods of dew or rain. Crop rotation with non-host crops reduces the severity of tan spot. Seed treatment seems to be effective in reducing the disease.
Fungicides applied timely are effective in reducing the disease severity and improving yield. Most fungicides are label to be applied up to Feekes 10.5 (fully headed) but before flowering. Only a couple of triazol fungicides are labeled to be applied for Fusarium Head Blight at 10.5.1, which is flowering.
Tan Spot can be serious by itself or it can contribute to other leaf spot complexes, like Stagnospora Glume Blotch, which we saw last year. This field has already been treated with a fungicide, and the pathogen is not highly infected our flag leaf. This is the leaf below the head which is pulling most of the photosynthate to the grain. This is what we are aiming to protect.